A randomized, open-label equivalence study of FTC versus lamivudine in HIV-1 infected patients with plasma HIV-1 RNA < 400 copies/ml on a stable antiretroviral therapy regimen containing lamivudine, stavudine or zidovudine, and a protease inhibitor (PI) or non-nucleoside reverse transcriptase inhibitor (NNRTI). Patients are considered stable if they have maintained a triple therapy for > 8 weeks if on a PI or > 12 weeks if on a NNTRI. 390 HIV-1 infected patients; at screening, patients must be stable on an antiretroviral therapy regimen containing lamivudine, stavudine or zidovudine, and a PI or NNRTI and have plasma RNA levels < 400 copies/ml. Patients are considered stable if they have maintained a triple therapy for > 8 weeks if on a PI or 12 weeks if on a NNRTI. During the study, HIV-1 RNA will be measured at Day 0 (baseline), weeks 2, 4, 8, 12, 16, 20, 24, 32, 36, 40, 44, and 48. Virologic success is defined as a continued suppression in HIV-1 RNA below 400 copies/ml. In each individual case, the insufficient virological response will have to be confirmed on two separate determinations within four weeks apart in the same laboratory. Tolerability failure is defined as any adverse event that is severe enough to warrent permanent discontinuation of FTC or Lamivudine. Patients will be randomized using central randomization in a 2:1 ratio to one of two treatment arms: Arm 1 (N+260) Switch lamivudine with FTC (200 mg qd) while continuing on current background regimen. Arm 2 (N=130) Continue on current lamivudine ( 150 mg bid) containing regimen. Patients will be stratified based upon screening plasma HIV-1 RNA and the background therapy as follows: Stratum 1 < 50 copies/mL; PI in treatment regimen. Stratum 2 < 50 copies/mL; NNTRI in treatment regimen. Stratum 3 50-400 copies/mL; PI in treatment regimen.Stratum 4 50-400 copies/mL; NNTRI in treatment regimen.